OSIRIS-REx Goes Asteroid Collecting · 2016. 9. 29. · mission Hayabusa, which returned the first...

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LUNAR AND PLANETARY INFORMATION BULLETIN • ISSUE 146, SEPTEMBER 2016 2

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OSIRIS-REx Goes Asteroid Collecting

— Scott Messenger, NASA Johnson Space Center

OSIRIS-REx is NASA’s third New Frontiers mission, following the New Horizons mission, which completed a flyby of Pluto in 2015, and the Juno mission to orbit Jupiter, which has just begun science operations. The OSIRIS-REx mission’s primary objective is to collect pristine surface samples of a carbonaceous asteroid and return them to Earth for analysis. Carbonaceous asteroids and comets are considered to be “primitive” bodies that have preserved remnants of the solar system

starting materials. By studying them, scientists can learn about the origin and earliest evolution of the solar system. The OSIRIS-REx spacecraft was launched on September 8, 2016, beginning its two-year journey to asteroid 101955 Bennu (formerly designated 1999 RQ36). After more than one year of detailed remote observations, OSIRIS-REx will obtain surface samples and return them to Earth in September 2023.

The OSIRIS-REx proposal, led by the late Dr. Michael J. Drake, was selected during the 2011 New Frontiers competition, and is now led by Dr. Dante Lauretta of the University of Arizona. The mission name OSIRIS-REx (an acronym for Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) embodies five objectives: (1) Origins: Return and analyze a sample of a carbonaceous asteroid; (2) Spectral Interpretation: Provide ground truth for remote observations of asteroids; (3) Resource Identification: Determine the mineral and chemical makeup of a near-Earth asteroid; (4) Security: Directly measure the non-gravitational force known as the Yarkovsky effect, which changes asteroidal orbits through its interaction with sunlight; and (5) Regolith Explorer: Determine the properties of unconsolidated material that covers the asteroid surface.

Motivation for Sample Return

Much of our knowledge of the origin and evolution of the solar system has been gleaned from the study of meteorites that are pieces of asteroids. Some asteroids such as (4) Vesta (the target of the ongoing Dawn mission) were large enough to “differentiate,” caused by internal heating that separated metal from silicate rocks. Other asteroids were not as strongly heated but were mainly affected by aqueous alteration. Primitive meteorites, like the CM chondrite shown on page 3, are rare and

The OSIRIS-REx mission used an Atlas V launch vehicle, built and operated by United Launch Alliance. The configuration used was the 411, which comprises a common core booster powered by Russian-built RD-180 engines with the RL-10C-powered Centaur sitting on top. Attached to the first stage is a single solid rocket booster, increasing the rocket’s throw capability to match the performance needed by OSIRIS-REx to reach asteroid Bennu. Credit: NASA.


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OSIRIS-REx Goes Asteroid Collecting continued . . .

fragile but have remained largely unchanged in the 4.5 billion years since the planets in our solar system formed. Studies have revealed interstellar materials within some meteorites that pre-date the solar system, high-temperature minerals that condensed from the solar nebula, and complex organic matter that formed in space and within asteroids. Laboratory analyses of these materials have led to new insights into the inner workings of stars, chemical processes in the galaxy, and the initial stages of planet formation. Moreover, asteroids may have been important contributors of water and organic matter to Earth early in its history.

The science value of meteorite studies is great, but faces some serious limitations. One of the most important problems is that, with very few exceptions, the parent asteroids of meteorites are not known. It is not known which meteorites share the same parent body. This challenge is not wholly unlike a geologist being given

a pile of rocks with no documentation of where they come from — or even what planet they come from — and being asked to construct their formation history and the origin of the solar system. Direct sample return from the surface of a well-characterized asteroid represents a whole new field of planetary science. Sample return makes it possible to connect global-scale observations and geological context with microscopic mineralogical and chemical properties. Together, these coordinated studies will bring a more complete understanding of how asteroids and the solar system formed and evolved.

Sample return can also circumvent the problem of terrestrial contamination that is particularly troublesome for studies of organic compounds. Most meteorites were recovered many years after they landed on Earth, and fresh meteorite “falls” sometimes occur in unfortunate locations such as farmland. Terrestrial weathering and contamination in our planet’s water- and organic-rich atmosphere quickly begin to take a toll on these precious samples as volatile materials are lost, minerals alter, and even terrestrial microorganisms take up residence. Of course, some of the most scientifically important organic compounds in meteorites are those that are common in biology, so it is not always possible to subtract out unknown contaminants from sample measurements. OSIRIS-REx will collect and return the most pristine samples of primitive asteroidal material ever available for study.

Finally, OSIRIS-REx will help to bridge the gap between remote spectroscopic studies of asteroids and the material properties of meteorites. Airless bodies like the Moon and asteroids are assaulted by radiation from the Sun and high-velocity impacts from interplanetary dust and larger bodies. These

OSIRIS-REx will return surface samples of the type of asteroid thought to be the parent body of the most primitive meteorites, carbonaceous chondrites. These asteroids are as dark as coal, suggesting that they are rich in carbon. Comparisons of the returned samples with meteorites and OSIRIS-REx’s remote observations of Bennu will help to identify the sources of primitive meteorites. The meteorite shown here is classified as a CM2 carbonaceous chondrite that was collected by the U.S.-led Antarctic Search for Meteorites (ANSMET) expedition to Antarctica in 1996.


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“space weathering” processes change the spectral properties of asteroids, complicating comparisons with meteorites. The recent successful Japanese mission Hayabusa, which returned the first samples from near-Earth asteroid Itokawa, proved the value of asteroid sample return. Analyses of dozens of tiny dust particles returned to Earth confirmed a link between S-type asteroids and the most common type of meteorites: ordinary chondrites. But the spectra of asteroids thought to be the most primitive are not well understood and are practically featureless. The return of samples from well-characterized, primitive asteroids by OSIRIS-REx and the already-flying Japanese mission Hayabusa2 will provide valuable new insight into the nature of the most-distant and perhaps best-preserved asteroids.

Why Bennu?

The OSIRIS-REx mission had to select the best target out of over 500,000 known asteroids in the solar system, with thousands more being discovered every year. It might seem that the target selection would be an overwhelming task, but technical limitations and scientific motivation quickly narrowed the choices. Most asteroids orbit the Sun between 2.2 and 3.2 astronomical units (AU), where 1 AU is the distance from the Sun to Earth. But asteroids beyond 1.6 AU from the Sun are out of reach for the OSIRIS-REx spacecraft, since it relies upon solar power. Other asteroids within 0.8 AU of the Sun reside in a realm in which it is more difficult for spacecraft to operate, and are likely to have some of their most interesting organic and water-rich materials cooked away in the intense sunlight. To select from among the remaining

7000 near-Earth asteroids, we needed to find asteroids that are easy to reach and easy to return from. After rejecting asteroids with orbits inclined to Earth’s orbital plane, noncircular orbits, or retrograde orbits, we were left with 192 potential targets.

The OSIRIS-REx sampling strategy requires us to be able to “hover” over the target surface, so we rejected rapidly rotating asteroids. Most of the accessible asteroids are so small (


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as being a very accessible, carbonaceous, well-studied asteroid.

Finally, Bennu is considered a hazardous asteroid, with an estimated 1-in-2700 chance of hitting Earth between the years 2175 and 2199. OSIRIS-REx observations will help to refine predictions of Bennu’s future orbit and revise impact probabilities. Global and microscale characterizations of Bennu will provide the information necessary to develop mitigation strategies and technology to protect our home planet from a potential impact.

The name Bennu was selected from more than eight thousand student entries from dozens of countries around the world who entered a “Name That Asteroid!” contest run by the University of Arizona, The Planetary Society, and the Lincoln Near Earth Asteroid Research (LINEAR) project. A third-grade student, Michael Puzio of North Carolina, proposed the name in reference to the Egyptian mythological bird Bennu, as he thought the spacecraft with its extended sample collection arm resembled the Egyptian deity, which is typically depicted as a heron.

Asteroid Bennu has a mean diameter of 492 meters (less than half a mile!), with a spheroidal, “spinning top” shape based on radar images. This is interpreted as a rubble-pile structure, where surface materials have gradually migrated to the equator. If this is true, then there is probably a lot of loose material on the surface suitable for sampling. Reflectance spectroscopy of Bennu show it is very dark, with an albedo of only 3–5 %. It is classified as a B-type asteroid, like the asteroid Themis, and is thought to have hydrated materials on its surface and abundant carbonaceous material. The closest meteorite analogs are the very rare CI and CM chondrites like Orgueil and Murchison, which are rich in hydrated minerals like clays and organic matter. These types of meteorites are very primitive and contain materials from the birth of the solar system, including the first generation condensates from the solar nebula, organic matter formed within the parent asteroid and interstellar clouds, and micrometer-sized grains of stardust.

Surveying Bennu

After arriving at asteroid Bennu, the OSIRIS-REx spacecraft will spend more than a year mapping surface structures, boulder and crater distributions, three-dimensional shape, gravity field, mineralogy, chemistry, and surface temperatures in order to thoroughly characterize the global geology of the asteroid and guide the selection of the sampling site. Four top-level maps will be produced to guide the sample site selection:

Diagram showing the orbit of asteroid Bennu. Credit: OSIRIS-REx Project/Dante Lauretta.


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• Safety: Asteroid surfaces pose various hazards for spacecraft, such as irregular slopes, boulders, and complex gravity fields. The team will consider these factors to identify no-go areas of Bennu that are unsafe for sample collection.

• Deliverability: This map will quantify how well the spacecraft can be navigated to the sample site. Asteroid Bennu will be so far from Earth that it will not be possible to fly the spacecraft remotely in real time, so the flight to the sample site will have to be done autonomously. Some areas of the asteroid may be too difficult to reach accurately unguided, especially in gravitationally or topographically complex areas.

• Sampling ability: OSIRIS-REx is designed to collect loose regolith: unconsolidated dust and rocks less than 2 centimeters in size. The remote surveys and detailed high-resolution images will be used to find areas that are suitable for satisfying the mission requirement to collect at least 60 grams of material.

• Science value: All areas of the asteroid surface are scientifically valuable, but the scientific priorities of OSIRIS-REx are the study of organic materials, water-rich phases, and presolar grains. The science value map will quantify the spectral evidence for various kinds of minerals

and organic phases as well as the surface geology and temperatures in order to identify the area on the asteroid that is most likely to satisfy this mission priority.

The OSIRIS-REx payload includes several instruments, which will be used to observe and characterize Bennu to generate the sample selection maps and for basic navigation. The OSIRIS-REx Camera Suite (OCAMS) is made up of three cameras that will perform low-resolution, long-range imaging, global mapping and imaging of the actual sampling site down to 1-centimeter spatial resolution. The OSIRIS-REx Laser Altimeter (OLA) is a scanning laser rangefinder that will be used to make a three-dimensional

topographic map of the entire asteroid. Higher-resolution three-dimensional maps will be taken of candidate sampling sites. The OSIRIS-REx Visible and Infrared Spectrometer (OVIRS) observes reflected light in the visible and near-infrared parts of the spectrum, in which characteristic absorption bands of the rock-forming minerals occur. The OSIRIS-REx Thermal Emission Spectrometer (OTES) is sensitive to longer infrared wavelengths, which contain information on both mineralogy and physical properties. Together, OVIRS and OTES will be used to map the abundance and distribution of organics and various minerals such as silicates, oxides, carbonates, and sulfates. The Regolith X-ray Imaging Spectrometer (REXIS) — a collaboration experiment developed by students from the Massachusetts Institute of Technology — is an X-ray imaging system that will develop a map of the elemental abundances on Bennu by measuring the fluorescent X-rays induced by sunlight and emitted from the asteroid surface.

The mapping of the near-Earth asteroid Bennu is one of the science goals of NASA’s OSIRIS-REx mission, and an integral part of spacecraft operations. The spacecraft will spend a year surveying Bennu before collecting a sample that will be returned to Earth for analysis. Credit: NASA/Goddard/University of Arizona.


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Touch-and-Go Sampling

The Touch-And-Go Sample Acquisition Mechanism (TAGSAM) is an aluminum and stainless steel cylinder about the diameter of a dinner plate mounted at the end of a long arm equipped with a strong spring like a pogo stick. The actual sample collection is relatively simple and will be over in just a few seconds. The spacecraft will slowly approach the sampling site with its sampling arm outstretched. Once pressure sensors detect surface contact, high-pressure ultra-pure nitrogen gas will be jetted into the regolith to mobilize it, directing rocks and dust into the collector like a reverse vacuum. A separate sample of fine-grained dust will be collected with stainless steel Velcro independent of the bulk-gas-mobilized sample. After five seconds, the spacecraft will retreat. Once the spacecraft has safely backed away, it will be rotated with its TAGSAM outstretched to measure the amount of mass collected. If it is determined that too little mass was collected, the spacecraft can support two more sampling attempts. Numerous groundbased tests and even tests onboard the microgravity “vomit comet” high-altitude aircraft show that the sampler is very effective and can collect as much as 1 kilogram (35 ounces) of material, an amount well in excess of the OSIRIS-REx mission requirement.

Coordinated Sample Studies

After verifying a successful surface sampling in July 2020, OSIRIS-REx will stow the sample in the Sample Return Capsule (SRC) for the journey home. OSIRIS-REx will fire its engines to start the return cruise in March 2021, returning to Earth in September 2023. Upon approach, the spacecraft will release the SRC for a fiery flight through Earth’s atmosphere at 12.4 kilometers per second (27,738 miles per hour). The heat shield will absorb more than 99% of this kinetic energy. After an ~3-kilometer (1.9-mile) free-fall, the SRC will deploy two parachutes to slow the descent and allow for a gentle landing at the Utah Test and Training Range (UTTR). The SRC will then be transported to NASA’s Johnson Space Center in Houston, where the samples will be initially examined and permanently curated and made available for study by investigators around the world.

The OSIRIS-REx payload includes a number of instruments designed to observe and characterize the asteroid Bennu, as well as provide basic navigation. Credit: OSIRIS-REx Project.

Blue arrows show how OSIRIS-REx will approach and contact Bennu to sample the surface. OSIRIS-REx carries three nitrogen bottles to facilitate three sample collection events with actual surface contact. Credit: OSIRIS-REx Project.


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The OSIRIS-REx science team will examine the returned samples to understand Bennu’s entire formation history in distinct astrophysical epochs. Bennu’s history began with the presolar epoch, as dust grains formed in the outflows of evolved stars and supernovae and complex chemistry took place in molecular clouds. This was followed by the nebular epoch, as grains condensed and aggregated to form planetesimals in the early solar system. We will examine the early geological history of Bennu, the later surface regolith processes, and finally its dynamical evolution over the “most recent” millions of years to its present orbit and configuration. The sample studies will be focused on addressing specific hypotheses, such as whether or not Bennu is related to known meteorites, or whether it contains abundant grains of stardust that predate the origin of the solar system. Specific study objectives include measuring the ages of individual, microscopic mineral grains; characterizing aqueous phases and how and when they formed; and identifying any prebiotic organic molecules and their formation processes.

From the Bennu samples, we will determine their mineralogy and petrology, elemental and isotopic compositions, organic chemistry, spectral properties, and thermal properties. These studies will be carried out with a range of sophisticated instruments such as transmission electron microscopy (TEM), electron microprobe, ion microprobe, infrared spectroscopy, liquid and gas chromatography, synchrotron particle accelerators, and laser ionization mass spectrometry. One of the challenges the team will face is to perform as many different types of analyses as possible with the same starting materials. Such coordinated analyses save sample mass and also benefit science by making it possible to link different properties together.

Another important objective of our studies will be to link the spectral and material properties of surface regolith grains with the remote observations of Bennu as a whole and from the sampling site. Reflectance spectra of Bennu samples measured in the laboratory will be compared with remote astronomical spectra of asteroids. Space exposure histories will be studied by measuring gas implanted from the solar wind and by the radiation damage from the Sun and galactic cosmic rays. The technique of TEM is capable of revealing radiation damage at the atomic scales, including the approximate energies and total dose of the radiation. By linking the remote astronomical observations of Bennu, the OSIRIS-REx remote sensing campaign, and the laboratory studies of returned samples, scientists hope to gain new insights into the properties and origins of thousands of asteroids throughout the solar system that remain mere points of light.

For more information about the OSIRIS-REx mission, visit the mission website at http://asteroidmission.org or the blog of the mission’s principal investigator at http://dslauretta.com.


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About the Author:

Scott Messenger, a scientist in the Astromaterials Research and Exploration Science (ARES) division of the NASA Johnson Space Center in Houston, Texas, is a co-investigator on the OSIRIS-REx mission. As lead of the Sample Analysis Working Group for the mission, Messenger is in charge of contamination knowledge studies of flight hardware to ensure the integrity of the collected samples. Messenger is also responsible for developing a coordinated sample analysis plan of the returned samples, and will study the

isotopic properties of the asteroidal samples with a NanoSIMS ion microprobe, a powerful mass spectrometer for measuring isotopic compositions of microscopic samples. He will determine the age of the samples and study the properties of ancient stardust grains and organic matter that predate the origin of the solar system.

Messenger received a B.S. in Astronomy and Physics from the University of Washington (1991) and a Ph.D. in Physics from Washington University in Saint Louis (1997). He joined NASA in 2003. His expertise is in isotopic analyses of extraterrestrial materials by secondary ion mass spectrometry (SIMS). His research interests include the nature and origin of materials in the solar nebula and preserved interstellar matter and stardust from comets and meteorites, and works closely with other researchers at ARES to coordinate isotopic studies with mineralogical studies by transmission electron microscopy and organic analyses by resonance ionization mass spectrometry and other spectroscopic techniques. He also took part in the analysis of cometary dust returned by the Stardust spacecraft in 2006.

About the Cover:

Top: A United Launch Alliance Atlas V rocket lifts off from Space Launch Complex 41 at Cape Canaveral Air Force Station, carrying NASA’s OSIRIS-REx spacecraft on the first U.S. mission to sample an asteroid. Liftoff was at 7:05 p.m. U.S. Eastern Daylight Time on Thursday, September 8. Credit: NASA/Sandy Joseph and Tim Terry.

Bottom left: The high-gain antenna and solar arrays were installed on the OSIRIS-REx spacecraft before it was moved to environmental testing in October. Credit: Lockheed Martin Corporation.

Bottom right: Artist’s concept of the OSIRIS-REx spacecraft near asteroid Bennu. Credit: NASA.

LUNAR AND PLANETARY INFORMATION BULLETIN • ISSUE 145, JUNE 2016 10

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The Lunar and Planetary Information Bulletin collects, synthesizes, and disseminates current research and findings in

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NASA Extends New Horizons and Other Planetary MissionsFollowing its historic first-ever flyby of Pluto, NASA’s New Horizons mission has received the green light to fly onward to an object deeper in the Kuiper belt, known as 2014 MU69. The spacecraft’s planned rendezvous with the ancient object — considered one of the early building blocks of the solar system — is January 1, 2019. “The New Horizons mission to Pluto exceeded our expectations, and even today the data from the spacecraft continue to surprise,” said NASA’s Director of Planetary Science, Jim Green. “We’re excited to continue onward into the dark depths of the outer solar system to a science target that wasn’t even discovered when the spacecraft launched.”

Based upon the 2016 Planetary Mission Senior Review Panel report, NASA directed nine extended missions to plan for continued operations through fiscal years 2017 and 2018. Final decisions on mission extensions are contingent on the outcome of the annual budget process. In addition to the extension of the New Horizons mission, NASA determined that the Dawn spacecraft should remain at the dwarf planet Ceres, rather than changing course to the main belt asteroid Adeona.

Green noted that NASA relies on the scientific assessment by the Senior Review Panel in making its decision on which extended mission option to approve. “The long-term monitoring of Ceres, particularly as it gets closer to perihelion (the part of its orbit with the shortest distance to the Sun) has the potential to provide more significant science discoveries than a flyby of Adeona,” he said.

Also receiving NASA approval for mission extensions are the Mars Reconnaissance Orbiter (MRO), Mars Atmosphere and Volatile EvolutioN (MAVEN), the Opportunity and Curiosity Mars rovers, the Mars Odyssey orbiter, the Lunar Reconnaissance Orbiter (LRO), and NASA’s support for the European Space Agency’s Mars Express mission.

News from Space

Artist’s impression of New Horizons’ close encounter with the Pluto-Charon system. Credit: NASA/JHU APL/SwRI/Steve Gribben.


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News from Space continued . . .

Philae Comet Lander Found!Less than a month before the end of the mission, Rosetta’s high-resolution camera has revealed the Philae lander wedged into a dark crack on Comet 67P/Churyumov-Gerasimenko. The images were taken on September 2 by the Optical, Spectral, and Infrared Remote Imaging System (OSIRIS) narrow-angle camera as the orbiter came within 2.7 kilometers (1.68 miles) of the surface and clearly show the main body of the lander, along with two of its three legs. The images also provide proof of Philae’s orientation, making it clear why establishing communications was so difficult following its landing on November 12, 2014.

“With only a month left of the Rosetta mission, we are so happy to have finally imaged Philae, and to see it in such amazing detail,” says Cecilia Tubiana of the OSIRIS camera team, the first person to see the images when they were downlinked from Rosetta on September 4. “After months of work, with the focus and the evidence pointing more and more to this lander candidate, I’m very excited and thrilled that we finally have this all-important picture of Philae sitting in Abydos,” added the European Space Agency’s (ESA’s) Laurence O’Rourke, who has been coordinating the search efforts over the last months at ESA, with the OSIRIS and Science

Operations and Navigation Center (SONC)/Centre National d’Etudes Spatiales (CNES) teams.

Philae was last seen when it first touched down at Agilkia, bounced and then flew for another two hours before ending up at a location later named Abydos, on the comet’s smaller lobe. After three days, Philae’s primary battery was exhausted and the lander went into hibernation, only to wake up again and communicate briefly with Rosetta in June and July 2015 as the comet came closer to the Sun and more power was available.

However, until today, the precise location was not known. Radio ranging data tied its location down to an area spanning a few tens of meters, but a number of potential candidate objects identified in relatively low-resolution images taken from larger distances could not be analyzed in detail until recently. While most candidates could be discarded from analysis of the imagery and other techniques, evidence continued to build toward one particular target, which is now confirmed in images taken unprecedentedly close to the surface of the comet. At 2.7 kilometers (1.68 miles), the resolution of the OSIRIS narrow-angle camera is about 5 centimeters/pixel (2 inches/pixel), sufficient to reveal characteristic features of Philae’s 1-meter-sized (3.3-foot-sized) body and its legs.

“This remarkable discovery comes at the end of a long, painstaking search,” says Patrick Martin, ESA’s Rosetta Mission Manager. “We were beginning to think that Philae would remain lost forever. It is incredible we have captured this at the final hour.”

Images taken by Rosetta’s high-resolution camera reveal the location of the Philae comet lander. Credit: Main image and lander inset: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; context: ESA/Rosetta/NavCam — CC BY-SA IGO 3.0.


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“This wonderful news means that we now have the missing ‘ground-truth’ information needed to put Philae’s three days of science into proper context, now that we know where that ground actually is!” says Matt Taylor, ESA’s Rosetta project scientist.

The discovery comes less than a month before Rosetta descends to the comet’s surface. On September 30, the orbiter will be sent on a final one-way mission to investigate the comet from close up, including the open pits in the Ma’at region, where it is hoped that critical observations will help to reveal secrets of the body’s interior structure (see the following article).

For more information, visit http://www.esa.int/Our_Activities/Space_Science/Rosetta or http://rosetta.jpl.nasa.gov/.

Rosetta Finale Set for September 30Rosetta is set to complete its mission in a controlled descent to the surface of its comet on September 30. The mission is coming to an end as a result of the spacecraft’s ever-increasing distance from the Sun and Earth. It is heading out toward the orbit of Jupiter, resulting in significantly reduced solar power to operate the craft and its instruments, and a reduction in bandwidth available to downlink scientific data. Combined with an aging spacecraft and payload that have endured the harsh environment of space for over 12 years — not least 2 years close to a dusty comet — this means that Rosetta is reaching the end of its natural life.

Unlike in 2011, when Rosetta was put into a 31-month hibernation for the most distant part of its journey, this time it is riding alongside the comet. Comet 67P/Churyumov-Gerasimenko’s maximum distance from the Sun (more than 850 million kilometers, or 528 million miles) is more than Rosetta has ever journeyed before. The result is that there is not enough power at its most distant point to guarantee that Rosetta’s heaters would be able to keep it warm enough to survive. Instead of risking a much longer hibernation that is unlikely to be survivable, and after consultation with Rosetta’s science team in 2014, it was decided that Rosetta would follow its lander Philae onto the comet.

The final hours of descent will enable Rosetta to make many once-in-a-lifetime measurements, including very-high-resolution imaging, boosting Rosetta’s science return with precious close-up data achievable

Close-up view of Comet 67P/Churyumov-Gerasimenko. During Rosetta’s final descent, the spacecraft will image the comet’s surface in high resolution from just a few hundred meters. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.

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only through such a unique conclusion. Communications will cease, however, once the orbiter reaches the surface, and its operations will then end.

“We’re trying to squeeze as many observations in as possible before we run out of solar power,” says Matt Taylor, ESA Rosetta project scientist. “30 September will mark the end of spacecraft operations, but the beginning of the phase where the full focus of the teams will be on science. That is what the Rosetta mission was launched for, and we have years of work ahead of us, thoroughly analyzing its data.”

Rosetta’s operators began changing the trajectory in August ahead of the grand finale such that a series of elliptical orbits will take it progressively nearer to the comet at its closest point. “Planning this phase is in fact far more complex than it was for Philae’s landing,” says Sylvain Lodiot, ESA Rosetta spacecraft operations manager. “The last six weeks will be particularly challenging as we fly eccentric orbits around the comet — in many ways this will be even riskier than the final descent itself. The closer we get to the comet, the more influence its non-uniform gravity will have, requiring us to have more control on the trajectory, and therefore more maneuvers — our planning cycles will have to be executed on much shorter timescales.”

A number of dedicated maneuvers in the closing days of the mission will conclude with one final trajectory change at a distance of around 20 kilometers (12 miles) about 12 hours before impact, to put the spacecraft on its final descent. The region to be targeted for Rosetta’s impact is still under discussion, as spacecraft operators and scientists examine the various trade-offs involved, with several different trajectories being examined. Broadly speaking, however, it is expected that impact will take place at about 50 centimeters/second (1.6 feet/second), roughly half the landing speed of Philae in November 2014.

Commands uploaded in the days before will automatically ensure that the transmitter as well as all attitude and orbit control units and instruments are switched off upon impact, to fulfill spacecraft disposal requirements. In any case, Rosetta’s high-gain antenna will very likely no longer be pointing toward Earth following impact, making any potential communications virtually impossible.

In the meantime, science will continue as normal, although there are still many risks ahead. Last month, the spacecraft experienced a “safe mode” while only 5 kilometers (3 miles) from the comet as a result of dust confusing the navigation system. Rosetta recovered, but the mission team cannot rule out this happening again before the planned end of the mission

“Although we’ll do the best job possible to keep Rosetta safe until then, we know from our experience of nearly two years at the comet that things may not go quite as we plan and, as always, we have to be prepared for the unexpected,” cautions Martin. “This is the ultimate challenge for our teams and for our spacecraft, and it will be a very fitting way to end the incredible and successful Rosetta mission.”


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NASA’s Juno Successfully Completes Jupiter FlybyNASA’s Juno mission successfully executed its first of 36 orbital flybys of Jupiter on August 27. The time of closest approach with the gas-giant world was 6:44 a.m. U.S. Pacific Daylight Time (13:44 UTC) when Juno passed about 4200 kilometers (2600 miles) above Jupiter’s swirling clouds. At the time, Juno was traveling at 208,000 kilometers per hour (130,000 miles per hour) with respect to the planet. This flyby was the closest Juno will get to Jupiter during its prime mission.

There are 35 more close flybys of Jupiter planned during Juno’s mission (scheduled to end in February 2018). The August 27 flyby was the first time Juno had its entire suite of science instruments activated and looking at the giant planet as the spacecraft zoomed past. “We are getting some intriguing early data returns as we speak,” said Scott Bolton, principal investigator of Juno from the Southwest Research Institute in San Antonio. “It will take days for all the science data collected during the flyby to be downlinked and even more to begin to comprehend what Juno and Jupiter are trying to tell us.”

While results from the spacecraft’s suite of instruments will be released down the road, a handful of images from Juno’s visible light imager, JunoCam, have already been released. Those images included the highest-resolution views of the jovian aurorae and the first glimpse of Jupiter’s north and south poles. “We are in an orbit nobody has ever been in before, and these images give us a whole new perspective on this gas-giant world,” said Bolton.

For more information, visit http://www.nasa.gov/juno or http://www.missionjuno.swri.edu.

Jupiter’s north polar region is coming into view as NASA’s Juno spacecraft approaches the giant planet. This view of Jupiter was taken on August 27, when Juno was 703,000 kilometers (437,000 miles) away. Credit: NASA/Southwest Research Institute.


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Dawn Maps Ceres Craters Where Ice Can AccumulateScientists with NASA’s Dawn mission have identified permanently shadowed regions on the dwarf planet Ceres. Most of these areas likely have been cold enough to trap water ice for a billion years, suggesting that ice deposits could exist there now. “The conditions on Ceres are right for accumulating deposits of water ice,” said Norbert Schorghofer, a Dawn guest investigator at the University of Hawaii at Manoa. “Ceres has just enough mass to hold on to water molecules, and the permanently shadowed regions we identified are extremely cold — colder than most that exist on the Moon or Mercury.”

Permanently shadowed regions do not receive direct sunlight. They are typically located on the crater floor or along a section of the crater wall facing toward the pole. The regions still receive indirect sunlight, but if the temperature stays below about –151°C (–240°F), the permanently shadowed area is a cold trap — a good place for water ice to accumulate and remain stable. Cold traps were predicted for Ceres but had not been identified until now.

In this study, Schorghofer and colleagues studied Ceres’ northern hemisphere, which was better illuminated than the south. Images from Dawn’s

cameras were combined to yield the dwarf planet’s shape, showing craters, plains, and other features in three dimensions. Using this input, a sophisticated computer model developed at NASA’s Goddard Space Flight Center was used to determine which areas receive direct sunlight, how much solar radiation reaches the surface, and how the conditions change over the course of a year on Ceres.

The researchers found dozens of sizeable permanently shadowed regions across the northern hemisphere. The largest one is inside a 16-kilometer-wide (10-mile-wide) crater located less than 65 kilometers (40 miles) from the north pole. Taken together, Ceres’ permanently shadowed regions occupy about 1800 square kilometers (695 square miles). This is a small fraction of the landscape — much less than 1% of the surface area of the northern hemisphere.

The team expects the permanently shadowed regions on Ceres to be colder than those on Mercury or the Moon. That’s because Ceres is quite far from the Sun, and the shadowed parts of its craters receive little indirect radiation. “On Ceres, these regions act as cold traps down to relatively low latitudes,” said Erwan Mazarico, a Dawn guest investigator at Goddard. “On the Moon and Mercury, only the permanently shadowed regions very close to the poles get cold enough for ice to be stable on the surface.”

The situation on Ceres is more similar to that on Mercury than the Moon. On Mercury, permanently shadowed regions account for roughly the same fraction of the northern hemisphere. The trapping efficiency — the ability to accumulate water ice — is also comparable.

At the poles of Ceres, scientists have found craters that are permanently in shadow (indicated by blue markings). Such craters are called “cold traps” if they remain below about –151°C (–240°F). Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.


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By the team’s calculations, about 1 out of every 1000 water molecules generated on the surface of Ceres will end up in a cold trap during a year on Ceres (1682 days). That’s enough to build up thin but detectable ice deposits over 100,000 years or so. “While cold traps may provide surface deposits of water ice as have been seen at the Moon and Mercury, Ceres may have been formed with a relatively greater reservoir of water,” said Chris Russell, principal investigator of the Dawn mission, based at the University of California, Los Angeles. “Some observations indicate Ceres may be a volatile-rich world that is not dependent on current-day external sources.”

The findings are available online in the journal Geophysical Research Letters. For more information, visit http://dawn.jpl.nasa.gov or http://www.nasa.gov/dawn.

What’s Inside Ceres? New Findings from Gravity DataIn the tens of thousands of photos returned by NASA’s Dawn spacecraft, the interior of Ceres isn’t visible. However, scientists have powerful data to study Ceres’ inner structure — Dawn’s own motion. Since gravity dominates Dawn’s orbit at Ceres, scientists can measure variations in Ceres’ gravity by tracking subtle changes in the motion of the spacecraft. Using data from Dawn, scientists have mapped the variations in Ceres’ gravity for the first time in a new study in the journal Nature, which provides clues to the dwarf planet’s internal structure.

“The new data suggest that Ceres has a weak interior, and that water and other light materials partially separated from rock during a heating phase early in its history,” said Ryan Park, the study’s lead author and the supervisor of the solar system dynamics group at NASA’s Jet Propulsion Laboratory (JPL).

Ceres’ gravity field is measured by monitoring radio signals sent to Dawn, and then received on Earth by NASA’s Deep Space Network. This network is a collection of large antennas at three locations around the globe that communicate with interplanetary spacecraft. Using these signals, scientists can measure the spacecraft’s speed to a precision of 0.1 millimeters (0.004 inches) per second, and then calculate the details of the gravity field.

Ceres has a special property called “hydrostatic equilibrium,” which was confirmed in this study. This means that Ceres’ interior is weak enough that its shape is governed by how it rotates. Scientists reached this conclusion by comparing Ceres’ gravity field to its shape. Ceres’ hydrostatic equilibrium is one reason why astronomers classified the body as a dwarf planet in 2006.

This artist’s concept shows a diagram of how the inside of Ceres could be structured, based on data about the dwarf planet’s gravity field from NASA’s Dawn mission. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.


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The data indicate that Ceres is “differentiated,” which means that it has compositionally distinct layers at different depths, with the densest layer at the core. Scientists also have found that, as they suspected, Ceres is much less dense than Earth, the Moon, the giant asteroid Vesta (Dawn’s previous target), and other rocky bodies in our solar system. Additionally, Ceres has long been suspected to contain low-density materials such as water ice, which the study shows separated from the rocky material and rose to the outer layer along with other light materials. “We have found that the divisions between different layers are less pronounced inside Ceres than the Moon and other planets in our solar system,” Park said. “Earth, with its metallic core, semi-fluid mantle, and outer crust, has a more clearly defined structure than Ceres,” Park said.

Scientists also found that high-elevation areas on Ceres displace mass in the interior. This is analogous to how a boat floats on water: The amount of displaced water depends on the mass of the boat. Similarly, scientists conclude that Ceres’ weak mantle can be pushed aside by the mass of mountains and other high topography in the outermost layer as though the high-elevation areas “float” on the material below. This phenomenon has been observed on other planets, including Earth, but this study is the first to confirm it at Ceres.

The internal density structure, based on the new gravity data, teaches scientists about what internal processes could have occurred during the early history of Ceres. By combining this new information with previous data from Dawn about Ceres’ surface composition, they can reconstruct that history: Water must have been mobile in the ancient subsurface, but the interior did not heat up to the temperatures at which silicates melt and a metallic core forms. “We know from previous Dawn studies that there must have been interactions between water and rock inside Ceres,” said Carol Raymond, a co-author and Dawn’s deputy principal investigator based at JPL. “That, combined with the new density structure, tells us that Ceres experienced a complex thermal history.”

After studying Ceres for more than eight months from its low-altitude science orbit, NASA’s Dawn spacecraft is now moving higher up for different views of the dwarf planet. Dawn has delivered a wealth of images and other data from its current perch at 385 kilometers (240 miles) above Ceres’ surface, which is closer to the dwarf planet than the International Space Station is to Earth. Now, the mission team is pivoting to consider science questions that can be examined from higher up.

After Dawn completed its prime mission on June 30, having surpassed all of its scientific objectives at Vesta and at Ceres, NASA extended the mission to perform new studies of Ceres. One of the factors limiting Dawn’s lifetime is the amount of hydrazine, the propellant needed to orient the spacecraft to observe Ceres and communicate with Earth. By going to a higher orbit at Ceres, Dawn will use the remaining hydrazine more sparingly, because it won’t have to work as hard to counter Ceres’ gravitational pull.

On September 2, Dawn began spiraling upward to about 1460 kilometers (910 miles) from Ceres. The altitude will be close to where Dawn was a year ago, but the orientation of the spacecraft’s orbit — specifically, the angle between the orbit plane and the Sun — will be different this time, so the spacecraft will have a different view of the surface.


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ESO Discovers Earth-Sized Planet in Habitable Zone of Nearest StarA newly discovered, roughly Earth-sized planet orbiting our nearest neighboring star might be habitable, according to a team of astronomers using the European Southern Observatory’s (ESO’s) 3.6-meter (11.8-foot) telescope at La Silla, Chile, along with other telescopes around the world. The exoplanet is at a distance from its star that allows temperatures mild enough for liquid water to pool on its surface.

“NASA congratulates ESO on the discovery of this intriguing planet that has captured the hopes and the imagination of the world,” says Paul Hertz, Astrophysics Division Director at NASA Headquarters. “We look forward to learning more about the planet, whether it holds ingredients that could make it suitable for life.”

The new planet circles Proxima Centauri, the smallest member of a triple star system known to science fiction fans everywhere as Alpha Centauri. Just over 4 light-years away, Proxima is the closest star to Earth, besides our own Sun. “This is really a game-changer in our field,” said

Olivier Guyon, a planet-hunting affiliate at NASA’s Jet Propulsion Laboratory (JPL), and associate professor at the University of Arizona, Tucson. “The closest star to us has a possible rocky planet in the habitable zone. That’s a huge deal. It also boosts the already existing, mounting body of evidence that such planets are near, and that several of them are probably sitting quite close to us. This is extremely exciting.”

The science team that made the discovery, led by Guillem Anglada-Escudé of Queen Mary University of London, published its findings on August 25 in the journal Nature. The team traced subtle wobbles in the star, revealing the presence of a star-tugging planet.

They determined that the new planet, dubbed Proxima b, is at least 1.3 times the mass of Earth. It orbits its star far more closely than Mercury orbits our Sun, taking only 11 days to complete a single orbit — a “year” on Proxima b. The stunning announcement comes with plenty of caveats. While the new planet lies within its star’s “habitable zone” — a distance at which temperatures are right for liquid water — scientists do not yet know if the planet has an atmosphere.

It also orbits a red-dwarf star, far smaller and cooler than our Sun. The planet likely presents only one face to its star, as the Moon does to Earth, instead of rotating through our familiar days and nights. And Proxima b could be subject to potentially life-extinguishing stellar flares.

“That’s the worry in terms of habitability,” said Scott Gaudi, an astronomy professor at Ohio State University, Columbus, and JPL affiliate credited with numerous exoplanet discoveries. “This thing

This artist’s impression shows a view of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the solar system. The double star Alpha Centauri AB also appears in the image. Credit: ESO/M. Kornmesser.


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is being bombarded by a fair amount of high-energy radiation. It’s not obvious if it’s going to have a magnetic field strong enough to prevent its whole atmosphere from getting blown away. But those are really hard calculations, and I certainly wouldn’t put my money either way on that.”

Despite the unknowns, the discovery was hailed by NASA exoplanet hunters as a major milestone on the road to finding other possible life-bearing worlds within our stellar neighborhood. “It definitely gives us something to be excited about,” said Sara Seager, a planetary science and physics professor at the Massachusetts Institute of Technology, Cambridge, and an exoplanet-hunting pioneer. “I think it will definitely motivate people to get moving.” Statistical surveys of exoplanets — planets orbiting other stars — by NASA’s Kepler space telescope have revealed a large proportion of small planets around small stars, she said.

The Kepler data suggest we should expect at least one potentially habitable, Earth-sized planet orbiting M-type stars, like Proxima, within 10 light-years of our solar system. So the latest discovery was “not completely unexpected. We’re more lucky than surprised,” Seager said. But it “helps buoy our confidence that planets are everywhere.”

It’s especially encouraging for upcoming space telescopes, which can contribute to the study of the new planet. The James Webb Space Telescope, launching in 2018, may be able to follow up on this planet with spectroscopy to determine the contents of its atmosphere. NASA’s Transiting Exoplanet Survey Satellite (TESS) will find similar planets in the habitable zone in the stellar backyard of our solar system in 2018. One of TESS’ goals is to find planets orbiting nearby M-dwarf stars like Proxima Centauri.

“It’s great news just to know that M-dwarf planets could be as common as we think they are,” Seager said. Another possible inspiration Proxima b could reignite: the admittedly far-off goal of sending a probe to another solar system.

Bill Borucki, an exoplanet pioneer, said the new discovery might inspire more interstellar research, especially if Proxima b proves to have an atmosphere. Coming generations of space- and groundbased telescopes, including large groundbased telescopes now under construction, could yield more information about the planet, perhaps inspiring ideas on how to pay it a visit.

“It may be that the first time we get really good information is from the newer telescopes that may be coming online in a decade or two,” said Borucki, now retired, the former principal investigator for Kepler, which has discovered the bulk of the more than 3300 exoplanets found so far. “Maybe people will talk about sending a probe to that star system,” Borucki said. “I think it does provide some inspiration for an interstellar mission because now we know there is a planet in the habitable zone, probably around the mass of Earth, around the closest star. I think it does inspire a future effort to go there and check it out.”

For more information, visit https://exoplanets.nasa.gov/.


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Pluto’s Methane Snowcaps on the Edge of DarknessThe southernmost part of Pluto that NASA’s New Horizons spacecraft could “see” during closest approach in July 2015 contains a range of fascinating geological features, and offers clues into what might lurk in the regions shrouded in darkness during the flyby. The area shown is south of Pluto’s dark equatorial band informally named Cthulhu Regio, and southwest of the vast nitrogen ice plains informally named Sputnik Planum or Sputnik Planitia, as the mission team recently redesignated the area to more accurately reflect the low elevation of the plains. North is at the top; in the western portion of the image, a chain of bright mountains extends north into Cthulhu Regio.

The mountains reveal themselves as snowcapped — something hauntingly familiar because of our Earth-based experience. However, New Horizons compositional data indicate the bright snowcap material covering these mountains isn’t water, but atmospheric methane that has condensed as frost onto these surfaces at high elevation. Between some mountains are sharply cut valleys, which are each a few miles across and tens of miles long.

A similar valley system in the expansive plains to the east appears to be branched, with smaller valleys leading into it. New Horizons scientists think flowing nitrogen ice that once covered this area — perhaps when the ice in Sputnik was at a higher elevation — may have formed these valleys. The area is also marked by irregularly shaped, flat-floored depressions that can reach more than 80 kilometers (50 miles) across and almost 3 kilometers (2 miles) deep. The great widths and depths of these depressions suggest that they may have formed when the surface collapsed, rather than through the sublimation of ice into the atmosphere.

The enhanced color image was obtained by New Horizons’ Multispectral Visible Imaging Camera (MVIC). The image resolution is approximately 680 meters (2230 feet) per pixel. It was obtained at a range of approximately 33,900 kilometers (21,100 miles) from Pluto, about 45 minutes before New Horizons’ closest approach to Pluto on July 14, 2015.

This area is south of Pluto’s dark equatorial band informally named Cthulhu Regio, and southwest of the vast nitrogen ice plains informally named Sputnik Planitia. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.


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Small Asteroid is Earth’s Constant CompanionA small asteroid has been discovered in an orbit around the Sun. Designated as 2016 HO3, the asteroid is a constant companion of Earth, and is likely to remain so for centuries to come. As it orbits the Sun, this new asteroid appears to circle Earth as well. It is too distant to be considered a true satellite of our planet, but it is the best and most stable example to date of a near-Earth companion, or “quasi-satellite.”

“Since 2016 HO3 loops around our planet, but never ventures very far away as we both go around the Sun, we refer to it as a quasi-satellite of Earth,” said Paul Chodas, manager of NASA’s Center for Near-Earth Object (NEO) Studies at the Jet Propulsion Laboratory. “One other asteroid — 2003 YN107 — followed a similar orbital pattern for a while over 10 years ago, but it has since departed our vicinity. This new asteroid is much more locked onto us. Our calculations indicate 2016 HO3 has been a stable quasi-satellite of Earth for almost a century, and it will continue to follow this pattern as Earth’s companion for centuries to come.”

In its yearly trek around the Sun, asteroid 2016 HO3 spends about half of the time closer to the Sun than Earth and passes ahead of our planet, and about half of the time farther away, causing it to fall behind. Its orbit is also tilted a little, causing it to bob up and then down once each year through Earth’s orbital plane. In effect, this small asteroid is caught in a game of leap frog with Earth that will last for hundreds of years.

The asteroid’s orbit also undergoes a slow, back-and-forth twist over multiple decades. “The asteroid’s loops around Earth drift a little ahead or behind from year to year, but when they drift too far forward or backward, Earth’s gravity is just strong enough to reverse the drift and hold onto the asteroid so that it never wanders farther away than about 100 times the distance of the Moon,” said Chodas. “The same effect also prevents the asteroid from approaching much closer than about 38 times the distance of the Moon. In effect, this small asteroid is caught in a little dance with Earth.”

Asteroid 2016 HO3 was first spotted on April 27, 2016, by the Pan-STARRS 1 asteroid survey telescope on Haleakala, Hawaii. The size of this object has not yet been firmly established, but it is likely larger than 40 meters (120 feet) and smaller than 100 meters (300 feet).

The Center for NEO Studies website has a complete list of recent and upcoming close approaches, as well as all other data on the orbits of known NEOs, so scientists and members of the media and public can track information on known objects. For more information, visit http://neo.jpl.nasa.gov/.

Asteroid 2016 HO3 has an orbit around the Sun that keeps it as a constant companion of Earth. Credit: NASA/JPL-Caltech.


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NASA’s Next Mars Rover Progresses Toward 2020 LaunchAfter an extensive review process and passing a major development milestone, NASA is ready to proceed with final design and construction of its next Mars rover, currently targeted to launch in the summer of 2020 and arrive on the Red Planet in February 2021. The Mars 2020 rover will investigate a region of Mars where the ancient environment may have been favorable for microbial life, probing the martian rocks for evidence of past life. Throughout its investigation, it will collect samples of soil and rock and cache them on the surface for potential return to Earth by a future mission.

“The Mars 2020 rover is the first step in a potential multi-mission campaign to return carefully selected and sealed samples of martian rocks and soil to Earth,” said Geoffrey Yoder, acting associate administrator of NASA’s Science Mission Directorate in Washington, DC. “This mission marks a significant milestone in NASA’s Journey to Mars — to determine whether life has ever existed on Mars, and to advance our goal of sending humans to the Red Planet.”

To reduce risk and provide cost savings, the 2020 rover will look much like its six-wheeled, one-ton predecessor, Curiosity, but with an array of new science instruments and enhancements to explore Mars as never before. For example, the rover will

conduct the first investigation into the usability and availability of martian resources, including oxygen, in preparation for human missions.

Mars 2020 will carry an entirely new subsystem to collect and prepare martian rocks and soil samples that includes a coring drill on its arm and a rack of sample tubes. About 30 of these sample tubes will be deposited at select locations for return on a potential future sample-retrieval mission. In laboratories on Earth, specimens from Mars could be analyzed for evidence of past life on Mars and possible health hazards for future human missions.

Two science instruments mounted on the rover’s robotic arm will be used to search for signs of past life and determine where to collect samples by analyzing the chemical, mineral, physical, and organic characteristics of martian rocks. On the rover’s mast, two science instruments will provide high-resolution imaging and three types of spectroscopy for characterizing rocks and soil from a distance, also helping to determine which rock targets to explore up close. A suite of sensors on the mast and deck will monitor weather conditions and the dust environment, and a ground-penetrating radar will assess subsurface geologic structure.

The Mars 2020 rover will use the same sky crane landing system as Curiosity, but enhancements will give it the ability to land in more challenging terrain, making more rugged sites eligible as safe landing

This image is from computer-assisted-design work on the Mars 2020 rover. The design leverages many successful features of NASA’s Curiosity rover, which landed on Mars in 2012, but also adds new science instruments and a sampling system to carry out new goals for the 2020 mission. Credit: NASA/JPL-Caltech.


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candidates. “By adding what’s known as range trigger, we can specify where we want the parachute to open, not just at what velocity we want it to open,” said Allen Chen, Mars 2020 entry, descent, and landing lead at NASA’s Jet Propulsion Laboratory (JPL). “That shrinks our landing area by nearly half.”

Terrain-relative navigation on the new rover will use onboard analysis of downward-looking images taken during descent, matching them to a map that indicates zones designated unsafe for landing. “As it is descending, the spacecraft can tell whether it is headed for one of the unsafe zones and divert to safe ground nearby,” said Chen. “With this capability, we can now consider landing areas with unsafe zones that previously would have disqualified the whole area. Also, we can land closer to a specific science destination, for less driving after landing.”

There will be a suite of cameras and a microphone that will capture the never-before-seen or -heard imagery and sounds of the entry, descent, and landing sequence. Information from the descent cameras and microphone will provide valuable data to assist in planning future Mars landings, and make for thrilling video. “Nobody has ever seen what a parachute looks like as it is opening in the martian atmosphere,” said JPL’s David Gruel, assistant flight system manager for the Mars 2020 mission. “So this will provide valuable engineering information.”

Microphones have flown on previous missions to Mars, including NASA’s Phoenix Mars Lander in 2008, but never have actually been used on the surface of the Red Planet. “This will be a great opportunity for the public to hear the sounds of Mars for the first time, and it could also provide useful engineering information,” said Mars 2020 Deputy Project Manager Matt Wallace of JPL.

Once a mission receives preliminary approval, it must go through four rigorous technical and programmatic reviews — known as Key Decision Points (KDP) — to proceed through the phases of development prior to launch. Phase A involves concept and requirements definition; Phase B is preliminary design and technology development; Phase C is final design and fabrication; and Phase D is system assembly, testing, and launch. Mars 2020 has just passed its KDP-C milestone.

“Since Mars 2020 is leveraging the design and some spare hardware from Curiosity, a significant amount of the mission’s heritage components have already been built during Phases A and B,” said George Tahu, Mars 2020 program executive at NASA Headquarters. “With the KDP to enter Phase C completed, the project is proceeding with final design and construction of the new systems, as well as the rest of the heritage elements for the mission.”

The Mars 2020 mission is part of NASA’s Mars Exploration Program. Driven by scientific discovery, the program currently includes two active rovers and three NASA spacecraft orbiting Mars. NASA also plans to launch a stationary Mars lander in 2018, InSight, to study the deep interior of Mars. For more information, visit http://mars.nasa.gov/mars2020.


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NASA Mars Orbiters Reveal Seasonal Dust Storm PatternAfter decades of research to discern seasonal patterns in martian dust storms from images showing the dust, the clearest pattern appears to be captured by measuring the temperature of the Red Planet’s atmosphere. For six recent martian years, temperature records from NASA Mars orbiters reveal a pattern of three types of large regional dust storms occurring in sequence at about the same times each year during the southern hemisphere spring and summer. Each martian year lasts about two Earth years.

“When we look at the temperature structure instead of the visible dust, we finally see some regularity in the large dust storms,” said David Kass of NASA’s Jet Propulsion Laboratory (JPL). He is the instrument scientist for the Mars Climate Sounder on NASA’s Mars Reconnaissance Orbiter and lead author of a report about these findings published in June by the journal Geophysical Research Letters. “Recognizing a pattern in the occurrence of regional dust storms is a step toward understanding the fundamental atmospheric properties controlling them,” Kass said. “We still have much to learn, but this gives us a valuable opening.”

Dust lofted by martian winds links directly to atmospheric temperature: The dust absorbs sunlight, so the Sun heats dusty air more than clear air. In some cases, this can be dramatic, with a difference of more than 35°C (63°F) between dusty air and clear air. This heating also affects the global wind distribution, which can produce downward motion that warms the air outside the dust-heated regions. Thus, temperature observations capture both direct and indirect effects of the dust storms on the atmosphere.

Improving the ability to predict large-scale, potentially hazardous dust storms on Mars would have safety benefits for planning robotic and human missions to the planet’s surface. Also, by recognizing patterns and categories of dust storms, researchers make progress toward understanding how seasonal local events affect global weather in a typical Mars year.

NASA has been operating orbiters at Mars continuously since 1997. The Mars Climate Sounder on Mars Reconnaissance Orbiter, which reached Mars in 2006, and the Thermal Emission Spectrometer on Mars Global Surveyor, which studied Mars from 1997 to 2006, have used infrared observations to assess atmospheric temperature. Kass and co-authors analyzed temperature data representative of a broad layer centered about 25 kilometers (16 miles) above the martian surface. That’s high enough to be more affected by regional storms than by local storms.

Most martian dust storms are localized, smaller than about 2000 kilometers (about 1200 miles) across and dissipating within a few days. Some become regional, affecting up to a third of the planet and persisting

This graphic presents martian atmospheric temperature data as curtains over an image of Mars taken during a regional dust storm. The temperature profiles extend from the surface to about 80 kilometers (50 miles) up. Temperatures are color coded, from –153°C (–243°F) (purple) to –23°C (–9°F) (red). Credit: NASA/JPL-Caltech.


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up to three weeks. A few encircle Mars, covering the southern hemisphere but not the whole planet. Twice since 1997, global dust storms have fully enshrouded Mars. The behavior of large regional dust storms in martian years that include global dust storms is currently unclear, and years with a global storm were not included in the new analysis. Three large regional storms, dubbed types A, B and C, all appeared in each of the six martian years investigated.

Multiple small storms form sequentially near Mars’ north pole in the northern autumn, similar to Earth’s cold-season arctic storms that swing one after another across North America. “On Mars, some of these break off and head farther south along favored tracks,” Kass said. “If they cross into the southern hemisphere, where it is mid-spring, they get warmer and can explode into the much larger Type A dust storms.”

Southern hemisphere spring and summer on modern-day Mars are much warmer than northern spring and summer because the eccentricity of Mars’ orbit puts the planet closest to the Sun near the end of southern spring. Southern spring and summer have long been recognized as the dustiest part of the martian year and the season of global dust storms, even though the more detailed pattern documented in the new report had not been previously described.

When a Type A storm from the north moves into southern-hemisphere spring, the sunlight on the dust warms the atmosphere. That energy boosts the speed of winds. The stronger winds lift more dust, further expanding the area and vertical reach of the storm. In contrast, the Type B storm starts close to the south pole shortly before the beginning of southern summer. Its origin may be from winds generated at the edge of the retreating south-polar carbon dioxide ice cap. Multiple storms may contribute to a regional haze.

The Type C storm starts after the B storm ends. It originates in the north during northern winter (southern summer) and moves to the southern hemisphere like the Type A storm. From one year to another, the C storm varies more in strength, in terms of peak temperature and duration, than the A and B storms do. For more information, visit http://mars.jpl.nasa.gov.

NASA Mars Rover Can Choose Laser Targets On Its OwnNASA’s Mars rover Curiosity is now selecting rock targets for its laser spectrometer — the first time autonomous target selection is available for an instrument of this kind on any robotic planetary mission. Using software developed at NASA’s Jet Propulsion Laboratory (JPL), Curiosity is now frequently choosing multiple targets per week for a laser and a telescopic camera that are parts of the rover’s Chemistry and Camera (ChemCam) instrument. Most ChemCam targets are still selected by scientists discussing rocks or soil seen in images the rover has sent to Earth, but the autonomous targeting adds a new capability.

During Curiosity’s nearly four years on Mars, ChemCam has inspected multiple points on more than 1400 targets by detecting the color spectrum of plasmas generated when laser pulses zap a target — more than 350,000 total laser shots at about 10,000 points in all. ChemCam’s spectrometers record the wavelengths seen through a telescope while the laser is firing. This information enables scientists to identify the


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chemical compositions of the targets. Through the same telescope, the instrument takes images that are of the highest resolution available from the rover’s mast.

Autonomous Exploration for Gathering Increased Science (AEGIS) software had previously been used on NASA’s Mars Exploration Rover Opportunity, although less frequently and for a different type of instrument. That rover uses the software to analyze images from a wide-angle camera as the basis for autonomously selecting rocks to photograph with a narrower-angle camera. Development work on AEGIS won a NASA Software of the Year Award in 2011. “This autonomy is particularly useful at times when getting the science team in the loop is difficult or impossible — in the middle of a long drive, perhaps, or when the schedules of Earth, Mars, and spacecraft activities lead to delays in sharing information between the planets,” said robotics engineer Tara Estlin, the leader of AEGIS development at JPL.

The most frequent application of AEGIS uses onboard computer analysis of images from Curiosity’s stereo Navigation Camera (Navcam), which are taken routinely at each location where the rover ends a drive. AEGIS selects a target and directs ChemCam pointing, typically before the Navcam images are transmitted to Earth. This gives the team an extra jump in assessing the rover’s latest surroundings and planning operations for upcoming days.

To select a target autonomously, the software’s analysis of images uses adjustable criteria specified by scientists, such as identifying rocks based on their size or brightness. The criteria can be changed depending on the rover’s surroundings and the scientific goals of the measurements.

NASA’s Curiosity Mars rover autonomously selects some targets for the laser and telescopic camera of its ChemCam instrument. For example, onboard software analyzed the Navcam image at left, chose the target indicated with a yellow dot, and pointed ChemCam for laser shots and the image at right. Credit: NASA/JPL-Caltech/LANL/CNES/IRAP/LPGNantes/CNRS/IAS.


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Another AEGIS mode starts with images from ChemCam’s own Remote Micro-Imager, rather than the Navcam, and uses image analysis to hone pointing of the laser at fine-scale targets chosen in advance by scientists. For example, scientists might select a threadlike vein or a small concretion in a rock, based on images received on Earth. AEGIS then controls the laser sharpshooting. “Due to their small size and other pointing challenges, hitting these targets accurately with the laser has often required the rover to stay in place while ground operators fine tune pointing parameters,” Estlin said. “AEGIS enables these targets to be hit on the first try by automatically identifying them and calculating a pointing that will center a ChemCam measurement on the target.”

From the top of Curiosity’s mast, the instrument can analyze the composition of a rock or soil target from up to about 7 meters (23 feet) away.

“AEGIS brings an extra opportunity to use ChemCam, to do more, when the interaction with scientists is limited,” said ChemCam Science Operation Lead Olivier Gasnault, at the Research Institute in Astrophysics and Planetology (IRAP), of France’s National Center for Scientific Research (CNRS) and the University of Toulouse, France. “It does not replace an existing mode, but complements it.”

The Curiosity mission is using ChemCam and other instruments on the rover as the vehicle investigates geological layers on lower Mount Sharp. The rover’s extended mission is analyzing evidence about how the environment in this part of Mars changed billions of years ago from conditions well suited to microbial life — if life ever existed on Mars — to dry, inhospitable conditions. For more information, visit http://mars.jpl.nasa.gov/msl.

Mars Gullies Likely Not Formed By Liquid WaterNew findings using data from NASA’s Mars Reconnaissance Orbiter show that gullies on modern Mars are likely not being formed by flowing liquid water. This new evidence will allow researchers to further narrow theories about how martian gullies form, and reveal more details about Mars’ recent geologic processes. Scientists use the term “gully” for features on Mars that share three characteristics in their shape: an alcove at the top, a channel, and an apron of deposited material at the bottom. Gullies are distinct from another type of feature on martian slopes, streaks called “recurring slope lineae” (RSL), which are distinguished by seasonal darkening and fading, rather than characteristics of how the ground is shaped. Water in the form of hydrated salt has been identified at RSL sites. The new study focuses on gullies and their formation process by adding composition information to previously acquired imaging.

Researchers from the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, examined high-resolution compositional data from more than 100 gully sites throughout Mars. These data, collected by the orbiter’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), were then correlated with images from the same spacecraft’s High Resolution Imaging Science Experiment (HiRISE) camera and Context Camera (CTX).

The findings showed no mineralogical evidence for abundant liquid water or its byproducts, thus pointing to mechanisms other than the flow of water — such as the freeze and thaw of carbon dioxide frost — as


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being the major drivers of recent gully evolution. The findings were published in Geophysical Research Letters.

Gullies are a widespread and common feature on the martian surface, mostly occurring between 30° and 50° latitude in both the northern and southern hemispheres, generally on slopes that face toward the poles. On Earth, similar gullies are formed by flowing liquid water; however, under current conditions, liquid water is transient on the surface of Mars, and may occur only as small amounts of brine even at RSL streaks. The lack of sufficient water to carve gullies has resulted in a variety of theories for the gullies’ creation, including different mechanisms involving evaporation of water and carbon dioxide frost.

“The HiRISE team and others had shown there was seasonal activity in gullies — primarily in the southern hemisphere — over the past couple of years, and carbon dioxide frost is the main mechanism they suspected of causing it. However, other researchers favored liquid water as the main mechanism,” said Jorge Núñez of Johns Hopkin’s Applied Physics Laboratory (APL), the lead author of the paper. “What HiRISE and other imagers were not able to determine on their own was the composition of

the material in gullies because they are optical cameras. To bring another important piece in to help solve the puzzle, we used CRISM, an imaging spectrometer, to look at what kinds of minerals were present in the gullies and see if they could shed light on the main mechanism responsible.”

Núñez and his colleagues took advantage of a new CRISM data product called Map-projected Targeted Reduced Data Records. It allowed them to more easily perform their analyses and then correlate the findings with HiRISE imagery.

“On Earth and on Mars, we know that the presence of phyllosilicates — clays — or other hydrated minerals indicates formation in liquid water,” Núñez said. “In our study, we found no evidence for clays or other hydrated minerals in most of the gullies we studied, and when we did see them, they were erosional debris from ancient rocks, exposed and transported downslope, rather than altered in more

The highly incised martian gullies seen in the top image resemble gullies on Earth that are carved by liquid water. However, when the gullies are observed with the addition of mineralogical information (bottom), no evidence for alteration by water appears. The pictured area spans about 3 kilometers (2 miles) on the eastern rim of Hale Crater. The High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter took the visible-light image. Color-coded compositional information added in the lower version comes from the same orbiter’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). Credit: NASA/JPL-Caltech/UA/JHUAPL.


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recent flowing water. These gullies are carving into the terrain and exposing clays that likely formed billions of years ago when liquid water was more stable on the martian surface.”

Other researchers have created computer models that show how sublimation of seasonal carbon dioxide frost can create gullies similar to those observed on Mars, and how their shape can mimic the types of gullies that liquid water would create. The new study adds support to those models.

And while seasonal dark streaks on Mars have become one of the hottest topics in interplanetary research, they don’t hold much water, according to the latest findings from another NASA spacecraft orbiting Mars. The new results from NASA’s Mars Odyssey mission rely on ground temperature, measured by infrared imaging using the spacecraft’s Thermal Emission Imaging System (THEMIS). They do not contradict last year’s identification of hydrated salt at these flows, which since their 2011 discovery have been regarded as possible markers for the presence of liquid water on modern Mars. However, the temperature measurements now identify an upper limit on how much water is present at these darkened streaks: about as much as in the driest desert sands on Earth.

When water is present in the spaces between particles of soil or grains of sand, it affects how quickly a patch of ground heats up during the day and cools off at night. “We used a very sensitive technique to quantify the amount of water associated with these features,” said Christopher Edwards of Northern Arizona University in Flagstaff. “The results are consistent with no moisture at all and set an upper limit at three percent water.”

The features, RSL, have been identified at dozens of sites on Mars. A darkening of the ground extends downhill in fingerlike flows during spring or summer, fades away in fall and winter, then repeats the pattern in another year at the same location. The process that causes the streaks to appear is still a puzzle. “Some type of water-related activity at the uphill end still might be a factor in triggering RSL, but the darkness of the ground is not associated with large amounts of water, either liquid or frozen,” Edwards said. “Totally dry mechanisms for explaining RSL should not be ruled out.”

Edwards and Sylvain Piqueux of NASA’s Jet Propulsion Laboratory (JPL) analyzed several years of THEMIS infrared observations of a crater-wall region within the large Valles Marineris canyon system on Mars. Numerous RSL features sit close together in some parts of the study region. Edwards and Piqueux compared nighttime temperatures of patches of ground averaging about 44% RSL features, in the area, to temperatures of nearby slopes with no RSL. They found no detectable difference, even during seasons when RSL were actively growing. The report of these findings by Edwards and Piqueux is available online in the journal Geophysical Research Letters.

There is some margin of error in assessing ground temperatures with the multiple THEMIS observations used in this study, enough to leave the possibility that the RSL sites differed undetectably from non-RSL sites by as much as 1°C (1.8°F). The researchers used that largest possible difference to calculate the maximum possible amount of water — either liquid or frozen — in the surface material.


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How deeply moisture reaches beneath the surface, as well as the amount of water present right at the surface, affects how quickly the surface loses heat. The new study calculates that if RSL have only a wafer-thin layer of water-containing soil, that layer contains no more than about 30 grams of water per kilogram of soil (1 ounce of water per 2 pounds of soil). That is about the same concentration of water as in the surface material of the Atacama Desert and Antarctic Dry Valleys, the driest places on Earth. If the water-containing layer at RSL is thicker, the amount of water per kilogram or pound of soil would need to be even less, to stay consistent with the temperature measurements.

Research published last year identified hydrated salts in the surface composition of RSL sites, with an increase during the season when streaks are active. Hydrated salts hold water molecules affecting the crystalline structure of the salt. “Our findings are consistent with the presence of hydrated salts because you can have hydrated salt without having enough for the water to start filling pore spaces between particles,” Edwards said. “Salts can become hydrated by pulling water vapor from the atmosphere, with no need for an underground source of the water.”

“Through additional data and studies, we are learning more about these puzzling seasonal features — narrowing the range of possible explanations,” said Michael Meyer. “It just shows us that we still have much to learn about Mars and its potential as a habitat for life.”

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